The 3GPP LTE is envisioned to be a key technology for the next-generation wireless communications. The LTE network, also known as Evolved Universal Terrestrial Radio Access Network (E-UTRAN), has been standardized by the 3GPP. In the LTE system, Orthogonal Frequency-Division Multiple Access (OFDMA) is adopted as the down-link transmission scheme, while Single-Carrier Frequency-Division Multiple Access (SC-FDMA) technology is used for the User Equipments (UE) to up-link access the station device (eNodeB).
In the LTE system, a cell search process is a process for performing time and frequency synchronization between a UE and a cell and detecting a cell ID. To enable the UE to quickly obtain the frequency and synchronization information, a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) are designed in the LTE system. Each cell is identified through the cell-ID information carried by in the primary synchronization signal and the secondary synchronization signal. In the LTE system, the Zadoff-Chu sequence (hereinafter referred to as ZC sequence) is used to generate a PSS sequence, and three cells in a cell group are differentiated by three groups of sequences with roots of 25, 29, and 34, respectively. For the sake of illustration, FIG. 1 illustrates a diagram of a frequency domain ZC sequence. As illustrated in FIG. 1, the ZC sequence has a length of 63, wherein 62 sub-carriers excluding s direct current (DC) carrier are modulated, while the direct current carrier at the central position is not modulated so as to avoid direct current components.
This ZC sequence has a good auto-correlation property, but has a very low cross-correlation property. In other words, its auto-correlation value is very high, but its cross-correlation value is relatively low. Based on this feature, a non-coherent detection algorithm may be used in PSS sequence detection. In other words, the PSS sequence may be detected by detecting the peak of coherent values.
FIG. 2 illustrates a diagram of PSS detection according to the prior art. As illustrated in FIG. 2, at a receiver (i.e., at a user equipment UE), the received vector is filtered by a filter, so as to filter out the content have no relation with the PSS and avoid interference from other sub-carriers to the PSS. Then, the coherent values between the obtained receiver vector and the three local ZC sequences are calculated.
In case of PSS, due to the correlation property unique to the ZC sequence, the detected PSS will be matched to a local ZC sequence; at this point, a partial peak appears in an output of the PSS root identification module; by using this peak, it may be exactly determined at the receiver which PSS sequence the receive vector is, thereby determining the cell-ID. In case that the PSS does not appear, the calculated maximum coherent value will be lower than the determination threshold Ti, and at this point, the start point index θ of the sequence is plus 1 to enter into the next operation.
Thus, in the existing PSS detection algorithm, all the three local sequences are compared with the received sequence one by one, so as to determine whether the receive vector matches one of the ZC sequences. Besides, although the PSS sequence transmission frequency in downlink transmission is not very high, which is once in 5 ms, it is required to detect all received symbols in a prior scheme, so as to prevent miss-detection to the PSS symbols. Because the PSS transmission frequency is relatively low, most of these detected symbols are data symbols. However, even so, it is still required to use the three local ZC sequences to determine whether a received symbol matches one of the ZC sequence, and the algorithm will continue detection on a following symbol until a mismatch is determined. Therefore, actually, most of the detection operations for PSS algorithms are consumed on these data symbols, instead of the PSS sequence. All of the above result in that such PSS detection algorithm greatly consumes the data processing capability at the receiver; therefore, it is a rather inefficient detection policy, which will seriously restrain the speed of UE access to a cell.
Therefore, there is an urgent need for an improved PSS detection scheme in the art.